it's actually incredibly straightforward to get a Card set up with a new OS: https://wiki.debian.org/ArmHardFloatChroot
err... then... err... copy that to a MicroSD card and... err.. that's it. done.
It is true that there has been (heated) discussions about what kind of image should be shipped with the Eoma68-A20 cards and a lot has been explained here at this list and with the updates at crowdsupply. Still it seems kind of unfair to point Zap in the direction of how to set up a root filesystem as it is obviously not the hard part. The hard parts are the mentioned mainline kernel bug somewhere after 4.7-rc1 and to get all or most of the hardware working with a mainline kernel or at least a custom kernel based on mainline and to make everything work smooth with vanilla Debian. Some minor issues can be the correct setup of U-boot, sd-card filesystems, kernel config, ... although we can probably copy from the Eoma68-A20-Sd-Card provided by Luke.
kind regards Pablo